Offset pallet lever for watch escapement

ABSTRACT

An improved escapement mechanism for a horological device, especially a watch, with an improved pallet lever construction for coupling a conventional escape wheel and balance wheel. The pallet lever is constructed so that it can be pivotably mounted on an axis that lies within the outer diameter of the balance wheel by means of an offset portion passing around the balance wheel. The pallet lever is preferably an integral plastic member.

ljnited States Patent [191 Wuthrich OFFSET PALLET LEVER FOR WATCH ESCAPEMENT [75] Inventor: Paul Wuthrich, Watertown, Conn.

[73] Assignee: Timex Corporation, Waterbury,

Conn.

[22] Filed: Feb. 19, 1974 [21] Appl. No.: 443,281

[52] U.S. CI. 58/121 R, 58/116 R, 58/117,

. 58/59, 58/28 D [51] Int. Cl. G04b 15/08 [58] Field of Search 58/28 D, 59, 79, 116-121 [56] References Cited UNITED STATES PATENTS 11/1913 Clouir 58/79 2/ 1969 Verde 2/1970 Wuhtrich 58/59 [111 3,834,155 51 Sept. 10, 1974 FOREIGN PATENTS 0R APPLICATIONS 371,999 10/1963 Switzerland 58/28 D 1,255,852 1/1961 France 58/28 D Primary ExaminerRichard B. Wilkinson Assistant Examiner-Vit W. Miska STRACT An improved escapement mechanism for a horological device, especially a watch, with an improved pallet lever construction for coupling a conventional escape wheel and balance wheel. The pallet lever is constructed so that it can be pivotably mounted on an axis that lies within the outer diameter of the balance wheel by means of an offset portion passing around the balance wheel. The pallet lever is preferably an integral plastic member.

7 Claims, 2 Drawing Figures SHEEI 10F 2 PAINIEOsEP 1 01914 BACKGROUND OF THE INVENTION This invention relates to an improved pallet lever construction offering greater flexibility in arranging components making up an escapement. There are numerous types of escapements which have been highly refined and are well known in the horological art. Most escapements employ an oscillating pallet lever to periodically release a toothed escape wheel by means of a pair of pallet arms on one end, and to provide driving impulses to an oscillating balance wheel through a forked arm cooperating with the balance wheel. Exemplary of such an escapement is US. Pat. No. 3,146,581 issued to Garbe on Sept. 1, 1964 and assigned to the present assignee. Pallet levers are usually made of metallic materials with jewels or metal pins serving as the escapement pallets, but pallet levers of plastic material have been suggested, as in US. Pat. No. 3,425,212 issued to Verde on Feb. 4, 1969.

In designing an escapement, the designer wishes to be free to arrange the locations of escape wheel and balance wheel and to have the freedom to locate the pivot point of the interconnecting pallet lever wherever he wants in order to reach an optimum ratio of center distances, from escape wheel axis to pallet lever axis versus balance wheel axis to pallet lever axis. Should the pallet lever axis fall within the outer diameter of the balance wheel, the designer has, in the past, had two choices. He must either redesign the escapement so that the pivot points lie outside of the balance wheel axis, or he must locate the pivot points both on the same side of the balance wheel by utilizing a separate bridge member, as seen in exemplary U.S. Pats. Nos. 764,137Leonard (July 5, 1904); Cloux (Nov. 26, 1963); and 3,492,808-Wuthrich (Feb. 3, 1970).

The improved pallet lever of the present invention allows the designer to place the pivot point of the pallet lever inside the outer diameter of the oscillating balance wheel and offers other improved features, as well, when it is manufactured in the preferred embodiment from a single plastic piece.

SUMMARY OF THE INVENTION Briefly stated, the invention comprises an improved pallet lever having a pair of pallet arms and a forked impulse arm and having a first portion pivotably mounted on one side of the balance wheel, an offset axial portion passing outside of the balance wheel diameter, and a third portion connected to the offset portion and providing the second pivotable mounting on the opposite side of the balance wheel. Preferably the afore-said three portions are part of a single molding of wear-resistant plastic.

Accordingly, one object of the present invention is to provide an improved pallet lever construction which is economical to manufacture as a plastic member.

Another object of the invention is to provide an im proved pallet lever construction which offers greater flexibility to the designer in locating-the pallet lever pivot axis.

DRAWING The invention will be more clearly understood by reference to the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a plan view of an escapement mechanism, and

FIG. 2 is an elevation view, in section, and with pertinent portions rotated into the plane of the drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of the drawing, portions of a conventional escape wheel are shown at l with teeth 2 formed to provide the usual functions, as set forth in the aforementioned US. Pat. No. 3,146,581, which is incorporated herein by reference. Briefly, however, the teeth 2 are provided with special banking surfaces 3 and inclined impulse faces 4. The escape wheel is urged in the direction indicated by the arrow by a gear train and spring mechanism (not shown).

A conventional oscillating balance wheel is shown at 5 with an inner hub 6 and outer rim 7 connected by spokes 8. Hub 6 is mounted on a balance staff 9 having an integral safety roller 10 with indented portion 10a. Also projecting axially from hub 6 is a roller pin 11 (See FIG. 2).

All of the aforementioned portions of the escapement mechanism are largely conventional and may be substantially modified without departing from the concept of the present invention. The improved pallet lever, which is the subject of the present invention, is seen to comprise a first portion 12 pivotably mounted on the top side of the balance wheel at an axis 13 lying inside the outer diameter of rim 7 of the balance wheel. This first portion includes a pair of pallet arms 14, 15 with pallets 16, 17 formed integrally therewith. Pallets 16, 17 have inclined impulse faces 16a, which alternately cooperate with impulse faces 4 of the escapement teeth. The first pallet lever portion 12 also has an impulse arm 18 with a flat section 18a terminating in a conventional forked end 19 arranged to cooperate with the roller pin 11. Impulse arm 18 also has an integral rib 18b terminating in a projection 20 which cooperates with the indentation 10a in the conventional manner.

The pallet lever has a second offset axially extending portion 21 which is preferably molded as an integral hollow column depending from one of the pallet arms 15. This is better seen by reference to FIG. 2 which is a developed or rotated projection giving some distortion of the shape of the parts, but illustrating the method of operation. The escape wheel 1, balance wheel 5, and pallet lever 12 are all pivotably mounted between opposed plate members, here frame plate 22 and bridge member 23. Escape wheel 1 is carried on shaft 24 via journal bearings 25. The balance wheel staff 9 oscillates in v-shaped jewel bearings 26, oscillatory counterforce being provided by the conventional hairspring 27.

The pallet lever also includes a third portion 28 which extends from the offset portion 21 under rim 7 on the opposite side of the balance wheel. A steel pin 29 provides a first pivotal mounting by extending from frame 22 into an aperture 30 in the portion 28 of the pallet lever. Similarly, a coaxial pin 31, extending from the bridge 23 into a recess 32 in the upper portion 12 of the pallet lever, provides a second pivotal mounting.

Operation In operation, the balance wheel 5 oscillates through v the combined action of the hairspring 27 and periodic impulses imparted to the roller pin 11 by impulse arm 18 of the pallet lever. The escape wheel 1 is periodically released by, and provides driving impulses to, the pallet arms. The pallet lever oscillates in the normal manner about axis 13. However because of the novel construction, the two co-axial pins 29, 31 about which it pivots can be'located within the effective outer diameter of balance wheel 5, i.e.', within the outer diameter of rim 7 or any projections therefrom. Of course, if the balance wheel is constructed such that it has only a partial outer rim, it is understood that the term outer diameter as used herein means the diameter of the outer reachof any oscillating portions of the balance wheel.

While it is preferred that the first, second and third portions of the pallet lever be all molded of a single plastic member, it is within the purview of the present invention to form the pallet lever of separate pieces, for example, by using metal plate members for portions 12 and 28 connected by a separate offset portion 21. Also it is possible to put the pallet arms on the bottom or third portion 28, leaving the impulse arm 19 on the top or first portion 12. This is especially feasible if the pallet lever is made up of separate pieces. However, the

integral plastic lever with hollow column is the preferred embodiment of the invention, is very rigid and provides an outstanding construction when molded from a single piece of wear-resistant plastic such as acetal glass-filled plastic. Also the use of integral pallets on the pallet arms using the aforesaid plastic material, provides a very economical pallet lever construction, by eliminating the usual jewels or pins. It is desired to cover in the appended claims all modifications which fall within the true spirit and scope of the invention.

What is claimed as new is:

1. An escapement for a horological device having a toothed escape wheel, an oscillatory balance wheel with portions oscillating through an arc with an outer diameter and a pivotable pallet lever periodically connected therebetween to controllably release the escape wheel by means of a pair of pallet arms and provide driving impulses to the balance wheel by means of an impulse arm,

said pallet lever comprising a first portion pivotably mounted on one side of the balance wheel within said outer diameter thereof, a second offset portion extending axially outside the outer diameter of the balance wheel, and a third portion pivotably mounted on the opposite side of the balance wheel from said first portion, said first, second, and third portions connected to provide a pallet lever with pivot points inside the outer diameter of the balance wheel and on opposite sides thereof.

2. The combination according to claim 1, wherein said first, second and third portions are made as an integral member of wear-resistant plastic.

3. The combination according to claim 1, wherein said first portion includes said pair of pallet arms and wherein said offset portion depends from one of said pallet arms.

4. The combination according to claim 1, wherein said first portion includes an impulse arm comprising a plastic member with a flat section terminating in a fork and an integral rib terminating in a projection, said fork and projection being adapted for cooperative association with portions of the balance wheel.

5. The combination according to claim 1, wherein said second portion is a hollow column of plastic material integrally formed with said first and second portions of the lever.

6. The combination according to claim 5, wherein said first portion includes an impulse arm comprising a flat section terminating in a fork and an integral rib section terminating in a projection, said fork and projection being adapted for cooperation with parts of the balance wheel.

7. The combination according to claim 5,wherein said first portion further includes pallet arms having projecting integral pallets adapted to cooperate with the teeth of said escape wheel. 

1. An escapement for a horological device having a toothed escape wheel, an oscillatory balance wheel with portions oscillating through an arc with an outer diameter and a pivotable pallet lever periodically connected therebetween to controllably release the escape wheel by means of a pair of pallet arms and provide driving impulses to the balance wheel by means of an impulse arm, said pallet lever comprising a first portion pivotably mounted on one side of the balance wheel within said outer diameter thereof, a second offset portion extending axially outside the outer diameter of the balance wheel, and a third portion pivotably mounted on the opposite side of the balance wheel from said first portion, said first, second, and third portions connected to provide a pallet lever with pivot points inside the outer diameter of the balance wheel and on opposite sides thereof.
 2. The combination according to claim 1, wherein said first, second and third portions are made as an integral member of wear-resistant plastic.
 3. The combination according to claim 1, wherein said first portion includes said pair of pallet arms and wherein said offset portion depends from one of said pallet arms.
 4. The combination according to claim 1, wherein said first portion includes an impulse arm comprising a plastic member with a flat section terminating in a fork and an integral rib terminating in a projection, said fork and projection being adapted for cooperative association with portions of the balance wheel.
 5. The combination according to claim 1, wherein said second portion is a hollow column of plastic material integrally formed with said first and second portions of the lever.
 6. The combination according to claim 5, wherein said first portion includes an impulse arm comprising a flat section terminating in a fork and an integral rib section terminating in a projection, said fork and projection being adapted for cooperation with parts of the balance wheel.
 7. The combination according to claim 5, wherein said first portion further includes pallet arms having projecting integral pallets adapted to cooperate with the teeth of said escape wheel. 